1. Field of the Invention
The invention relates to an alignment mark, and more particularly, to an alignment mark fabricated by ion implantation processes and defect inspection for using the alignment mark.
2. Description of the Prior Art
Semiconductor integrated circuits undergo a variety of processing steps during manufacture, such as masking, resist coating, etching, and deposition. In many of these steps, material is overlaid or removed from the existing layer at specific locations in order to form the desired elements of the integrated circuit. Proper alignment of the various process layers is therefore critical.
Registration is typically used to measure layer-to-layer alignment accuracy for a semiconductor process. Registration involves comparing a position of a subsequent layer to a position of an existing layer by overlaying a distinct pattern on a matching pattern that is previously formed on the existing layer. At least an alignment mark is formed in the distinct pattern and the matching pattern. A distance between the alignment mark in the subsequent layer and the alignment mark in the existing layer provides a measure of misalignment between these two layers. Currently available registration structures include Box-in-Box visual verniers and Bar-in-Bar visual verniers to determine the extent of registration, i.e., the amount of alignment offset.
However, with the shrinking dimensions of modern integrated circuits, multi-layer structure is developed for a chip. For a three-layer structure or a more complicated structure, a plurality of layer-to-layer alignment and defect inspection is commonly performed. For instance, an optical defect inspection is performed on the wafer, and an electrical defect inspection is performed thereafter. Results from the defect inspection are then examined and compared according to defect map generated during the defect inspection. However, as different types of defect inspection use different coordinates, offset issue often arise from the values generated from the defect inspection and result in poor overlap sensitivity from layer-to-layer.